Tanning



Patented Jan. 16, 1945' I 2,367,589 TANNING Elbert C. Ladd, Pascale. N. 1., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application May 13, 1942. Serial No. 442,849

3 Claims.

This invention relates to improvements in tanning agents and methods of tanning skins and hides.

Both vegetable and chrome tanning are known methods of producing leather from raw hides. It is also known to use materials known as Syntans'! a auxiliary tanning agents. The Syntans are condensation products of monohydroxyaryl sulionic acids with aldehydes. It is also known that quinones themselves can be used as tannine, agents and such use is described in the literature (for example, J. A. Wilson, 'fModern Practice in Leather Manufacturingpages 434-435). Simple quinones are not satisfactory tanning agents in that they arerelatively insoluble in water and difiicult to handle due to irritating sible to use my improved tanning material in conjunction with other known tanning agents without the necessity of drastic changes in the pH conditions of the tanning liquor.

' tanning materials such as sulfited lignins.

eflects on the eyes and nasal passages. For these reasons quinone tanning as such has been of only theoretical interest, and according to recognized authorities in the field, it has never been of any commercial importance. I am also aware that both quinone sulfonic acid and sulfonated'hydroquinone have been employed as leather tannins agents, but both these materials are less active than benzoquinone itself since it requires from 1 to 2 /2 times as much benzoquinone sulfonlc acid as of benzoquinone to obtain suitable tanning action.

In an attempt to overcome the disadvantages of the prior methods oftanning,I have produced new leather tanning agents, consisting of 1.4-

benzcquinone thiosulfuric acid and its salts. The

1,4-benzoquinone 2-thiosulfuric acid or salt thereof is surprisingly considerably more active as a tanning agent than the corresponding sulfonic acid derivative and is further characterized by being free from the disadvantages possessed :by

benzoquinone itself.

iy concentrated tan liquors without the disadvantages resulting from the-use or concentrated vegetable tanning materials. Furthermore, the nature of my tanning material is such'as to cause it to penetrate very rapidly into thick hides. This 'is a particular advantage in the tanning or sdleleather.

- The optimum pH rang for tanning with my material cor'responds very closely to the optimum pH range for the tanning with either chrome My new tanning agents also appear to increase the effectiveness of tanning assistants or By the use of a combination of my tanning agent and a sulfited lignin, it is possible to obtain a superior grade of leather.

The chemicals may be prepared in several ways, among them being the following:

By reacting quinone with a thiosulfate, thereby obtaining a hydroquinone with an attached thiosulfate radical. This compound may then be suitably oxidized to give the corresponding quinone thiosulfuric acid or salt.

The following examples are given in detail to I illustrate the invention, but are not to be understood as limiting thereof:

Example 1 The potassium salt of 1,4-benzoquinone-2-thiosulfuric acid was prepared according to the meth- A tanning bath was prepared by dissolving 25 grams of the above reaction product in 250 cc. of water at F. The resulting pH of the solution was 2.9. A piece of acetone-dried raw calfskin weighing 53.8 grams was soaked in water untiliiully saturated, whereupon the wet weight was found to be 240grams. The skin was then 1 immersed in the tanning solution and the containing vessel wasrotated for 3 days. The 'pH was now 4.6. The skin was removed. and slicked free of excess' water, washed in running water for 20 hours and again .slicked free 01' excess wa-' ter. The weight was now 212- grams. (Shrink temperature was found to be 73 6., compared then washed-in water "at F. -1'or one-half with 64' C. for the rawhide.) The skin was bleaced as follows: 2 grams :01 sodium borate were dissolved in oneliter of water. The skin was shaken in this solution for 15 minutes and hour. The skin was then shaken in a solution or vegetable tanning materials. Thus it is po'sor 2 cc. concentrated H3804, in 800 cc. H 0

for 5 minutes, again washed with H2O at 100 F. for one-half hour. It was then fat-liquored in a solution of 16 grams of commercial tan oil in 800 cc. of water at 120 F. for 15 minutes. The pH 01 the fat-liquoring solution was adjusted to 2.7 b addition of H2804. The skin was then slicked free of excess oil and allowed to dry at room temperature over night, fat-liquored in a solution of 8 grams of tan oil in 800 cc. of water, slicked and allowed to dry over night. It

was then buffed on the flesh Side and soaked in water. After having been soaked until thoroughly saturated, it was slicked free of excess fluids and the grain side rubbed with olive oil and set out to dry. After drying over night, it was staked on a knee staker. The resulting product was a well-tanned piece of leather of good quality.

As further evidence of the tanning ability of the above relatively soluble quinone derivative, the following test shows the efiect of variations in pH on the tanning efliciency of the quinone derivatives.

Acetone-dried raw calfskin strips weighing. approximately 2.5 grams each were used for determination of shrink temperatures. Before being used, they were thoroughly soaked in distilled method outlined in the Journal of the American Leather Chemists Association 36, 681-2 (1941), except that water instead of glycerine was used as the heat transfer medium. The shrink temperature of the treated skin was 78 C. The shrink temperature of the untreated control strip was 66 C. The difierence in shrink temperature, namely, an increase of 12 C. is taken as an indication of tannage.

The above test was repeated a number of times with the pH of the liquor adjusted to a difierent value for each testby adding either 0.1- N HCl or 0.1- N NaOH to the liquor prior to starting the tanning operation. The results are recorded below:

Grams potassium salt or l,4 ben- Initial Final Shrink mm s. s a 5 63 The data show that our quinone tanning agent increases the shrink temperature of raw hides when used in tanning baths having considerable variations in pH, and that it is particularly effective in baths having pHs in the range 3.5 to 4.5.

A similar series or tests were run, using the sodium'salt of 1,4-benzoquinone-2-sulfonic acid, and in all cases the shrink temperature was 6 to 10 degrees lower, thus indicating inferior tanning behavior as compared to my invention.

Another recognized test of tanning ability is to determine the amount of tanning substance combined per grams of hid powder. In such a test, it was'found that as much as 18 grams of the 1,4-benzoquinone thiosulfate may be combined with 100 grams of hide powder.

Example 2 The tanning agents of my invention may be used in conjunction with other materials which either are tanning agents in themselves or have an auxiliary action. For example, a tanning bath containing the com und prepared in Example 1 together with -a commercial lignosulfonlc acid sold under the name of Super-Spruce" was prepared by dissolving 6.25 grams of the potassium salt of 1,4-benzoquinone-2-thiosulfuric acid and 25 grams of Super-Spruce in 250 grams of water. The resulting pH was noted to be 2.6. A piece of acetone-dried rawcalfskin weighing 51.7 grams was soaked in water until saturated then slicked free of excess H2O (wet weight 226 grams). It was then placed in the tan liquor and agitated for 72 hours. The skinwas then Worked up in the same way as described in Example 1. The result was a piece of well-tanned leather of good quality.

It is to be understood that the tanning materials do not have to be isolated from the solutions in which they are prepared. One may also prepare a tanning liquor, for example, by oxidizing any suitably substituted benzene thiosuliuric acid or salt thereof in an aqueous medium to obtain an aqueous solution of a 1,4-quinon thiosulfuric acid or salt thereof. Such solution can be used directly as the tanning liquors. Various 1 oxidizing agents may be used in the preparation of these derivatives. For example, one may use a chromium compound such as sodium dichromate or chromic anhydride as the oxidizing agent. The tan liquor prepared by such a reaction will contain both the desired benzoquinone derivative and the chromium salt, the latter being in a suitable state to produce tanning effects. Such a solution, therefore, will provide a tanning action due to both a chromium salt and the soluble quinone derivative.

The invention is not limited to the methods of preparation used in the illustration. Other methods of preparing the quinone derivatives are known and may be used. For example, paraaminophenol-ortho-thiosulfuric acid, or a salt thereof, can be oxidized in an aqueous medium to produce a solution of the quinone derivative, which solution is an efiective tanning liquor.

It is to be understood that the invention is not to be limited to the compounds given in the examples. Although it appears that the tanning action is due primarily to the quinone thiosul-' furic acid, or a salt thereof, other products may be formed during the oxidation, which may aid in the tanning action. For example, quinones are known to form complexes with hydroquinones. Furthermore, controlled oxidation of a hydroquinone (or controlled reduction of a quinone) may lead to complex derivatives. One type of such complexes is known as a quinhydrone. It is possible that such complexes are formed by methods herein described and that they may contribute to the tanning action. Such derivatives may be formed by methods used in preparing the quinone derivatives and are understoodto be within the broad scope 01' my invention. For this reason the present products are generally defined as oxidation products of substituted benzene thiosulfuric acids, and their salts, which substituted acids and salts have the property of being oxidized to quinone thiosulfuric acids, or their salts. The more common substituents in the aryl nucleus, which on oxidation provide the final quinonenucleus, include dihydroxy, amino, di-amino, etc., radicals.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A method of tanning skins or hides which comprises immersing the same in an acid bath containing a tanning agent comprising an oxidation product of 1,4 substituted benzene 2-thiosulfuric acids, and their salts, which substituted acids and salts have the property of being oxidizable to the corresponding quinone thiosulfuric acid, and their salts, respectively.

2. A method of tanning skins or hides which comprises immersing the same in an acid bath containing a tanning agent comprising a compound having the general formula 

